1. Technical Field of the Invention
The present invention relates generally to a vibration damping apparatus for automotive vehicles, and more particularly to a vibration damping apparatus operable to minimize vibration transmitted to a vehicle body caused by engine rotation.
2. Background Art
Japanese Patent First Publication No. 61-65023 discloses a vibration control system for reducing torque variation of an internal combustion engine utilizing an electric generator and an electric motor which are arranged respectively to provide additional torque to the engine and consume part of engine torque. This conventional system is designed to detect engine speed to control operation switching timing between the electric generator and the electric motor based thereon. When the engine torque is high, the electric generator provides a reverse torque to eliminate an excess of the engine torque, while, when the engine torque is low, the electric motor provides additional torque to compensate a lack of the engine torque. The operation switching timing between the electric generator and the electric motor are selected according to the detected engine speed based on the fact that the engine is subjected to the variation in combustion torque when the engine speed is high, while the engine undergoes the variation in inertial torque caused by piston movement when the engine speed is low, and the phase of the variation in torque is changed according to the engine speed.
Generally, the vehicle vibrations consist of a rotational vibration component (i.e., a torque variation component) caused by reaction of a small variation in speed of a crankshaft and a vertical vibration component produced by reaction of vertical displacement of a piston. The above prior art torque vibration control system thus, raises a drawback in that although the variation in engine torque, or the rotational vibration component developed by the reaction of the small variation in speed of the crankshaft may be minimized, the vertical vibration component is not reduced.